Chemically modified Poly-Vinyl-Chloride compositions are numerous and well-known. The usual approach to modification of this polymer is by means of grafting onto the macromolecule of various other reactive monomers, or telomers, or other entities, by chemical, photochemical or radiation initiation. Processes of this kind are well documented. Thus, A. Chapiro, in his book "Radiation Chemistry of Polymeric System," New York Interscience, V., 15, 1962, extensively quotes many cases of radiation grafting of various monomers to P.V.C. More recently, Kennedy has developed a general method for the chemical grafting of certain monomers to P.V.C., using an alkyl-aluminium catalyst (Cationic Graft Copolymerization, J. P. Kennedy, Editor-Interscience, 1977).
All these methods lack practicality, and no commercial application has, to our knowledge, resulted from these and similar approaches for several reasons. Radiation-grafting requires expensive and cumbersome equipment, as well as elaborate safety precautions. The catalytic methods of Kennedy involve the use of expensive and dangerous-to-handle metallo-organic compounds. In addition, to effect a grafting reaction on P.V.C. in accordance with the various methods described in the literature, the P.V.C. has to be dissolved in an organic anhydrous solvent, such as cyclohexanone, or tetrahydrofuran, forming very viscous solutions even at quite low concentrations, which are extremely difficult to handle in a chemical reaction. This is the main reason why previous attempts to modify P.V.C. by grafting reactions remain to-date a laboratory exercise only.
The interest in graft-modified P.V.C. is very considerable. This is spurred by the various well-known shortcomings of neat Poly(Vinyl-Chloride), especially when intended for certain particular uses. Thus, P.V.C. is largely being used in a highly plasticized form, for the production of films, tubing, coatings, etc. The common plasticizers used are the various phthalate esters, and particularly di-2-ethylhexyl phthalate--lack in "permanence" and tend to exude in time from the polymer composition, leaving an embrittled, friable object. The extraction of plasticizer--which does not form a chemical bond with the macromolecule--is particularly accelerated by contact with various solvents that leach it out from the polymer matrix. Such plasticized compositions are, therefore, restricted to use in solventless environments.
As a result of the possible exudation of the phthalate plasticizers these compositions have lately become a subject for review, since they have been shown in induce tumors in the liver of mice (cf. C and EN p. 5, May 5, 1980).
Another well-known drawback of commercial P.V.C. compositions is their hydrophobic nature. This results in the accumulation of static electricity, and the easy deposition of dust, which in certain applications (music records, greenhouse coverings, textile fibers) is very deleterious.